Pass logger pointer around instead of copying the struct

This is to remove flakes in test like
(https://buildpacks.ci.cf-app.com/teams/feature-eng/pipelines/npm-cnb/jobs/integration-tests/builds/4)
The writer doesn't seem to show deterministic write behavior
when logging using copies of logger. Hence pass a pointer
to the same logger around.

cmd/build/main.go

@@ -16,8 +16,8 @@ func main() {
 	logger := scribe.NewLogger(os.Stdout)
 
 	checksumCalculator := fs.NewChecksumCalculator()
-	resolver := npm.NewBuildProcessResolver(executable, checksumCalculator, logger)
+	resolver := npm.NewBuildProcessResolver(executable, checksumCalculator, &logger)
 	clock := npm.NewClock(time.Now)
 
-	packit.Build(npm.Build(resolver, clock, logger))
+	packit.Build(npm.Build(resolver, clock, &logger))
 }

npm/build.go

@@ -21,7 +21,7 @@ type BuildManager interface {
 	Resolve(workingDir, cacheDir string) (BuildProcess, error)
 }
 
-func Build(buildManager BuildManager, clock Clock, logger scribe.Logger) packit.BuildFunc {
+func Build(buildManager BuildManager, clock Clock, logger *scribe.Logger) packit.BuildFunc {
 	return func(context packit.BuildContext) (packit.BuildResult, error) {
 		logger.Title("%s %s", context.BuildpackInfo.Name, context.BuildpackInfo.Version)
 

npm/build_process_resolver.go

@@ -29,10 +29,10 @@ type Summer interface {
 type BuildProcessResolver struct {
 	executable Executable
 	summer     Summer
-	logger     scribe.Logger
+	logger     *scribe.Logger
 }
 
-func NewBuildProcessResolver(executable Executable, summer Summer, logger scribe.Logger) BuildProcessResolver {
+func NewBuildProcessResolver(executable Executable, summer Summer, logger *scribe.Logger) BuildProcessResolver {
 	return BuildProcessResolver{
 		executable: executable,
 		summer:     summer,

npm/build_process_resolver_test.go

@@ -45,7 +45,7 @@ func testBuildProcessResolver(t *testing.T, context spec.G, it spec.S) {
 		buffer = bytes.NewBuffer(nil)
 		logger := scribe.NewLogger(buffer)
 
-		resolver = npm.NewBuildProcessResolver(executable, summer, logger)
+		resolver = npm.NewBuildProcessResolver(executable, summer, &logger)
 	})
 	it.After(func() {
 		Expect(os.RemoveAll(workingDir)).To(Succeed())
@@ -258,7 +258,8 @@ func testBuildProcessResolver(t *testing.T, context spec.G, it spec.S) {
 			workingDir, err = ioutil.TempDir("", "working-dir")
 			Expect(err).NotTo(HaveOccurred())
 
-			resolver = npm.NewBuildProcessResolver(executable, summer, scribe.NewLogger(bytes.NewBuffer(nil)))
+			logger := scribe.NewLogger(bytes.NewBuffer(nil))
+			resolver = npm.NewBuildProcessResolver(executable, summer, &logger)
 		})
 
 		it.After(func() {

npm/build_test.go

@@ -79,7 +79,7 @@ func testBuild(t *testing.T, context spec.G, it spec.S) {
 		buffer = bytes.NewBuffer(nil)
 		logger := scribe.NewLogger(buffer)
 
-		build = npm.Build(buildManager, clock, logger)
+		build = npm.Build(buildManager, clock, &logger)
 	})
 
 	it.After(func() {
@@ -239,7 +239,8 @@ func testBuild(t *testing.T, context spec.G, it spec.S) {
 				return nil
 			}
 
-			build = npm.Build(buildManager, clock, scribe.NewLogger(buffer))
+			logger := scribe.NewLogger(buffer)
+			build = npm.Build(buildManager, clock, &logger)
 		})
 
 		it("filters out empty layers", func() {
@@ -283,7 +284,8 @@ func testBuild(t *testing.T, context spec.G, it spec.S) {
 		it.Before(func() {
 			buildProcess.RunCall.Stub = func(ld, cd, wd string) error { return nil }
 
-			build = npm.Build(buildManager, clock, scribe.NewLogger(buffer))
+			logger := scribe.NewLogger(buffer)
+			build = npm.Build(buildManager, clock, &logger)
 		})
 
 		it("filters out empty layers", func() {